Hi All. Building a '71 455" (Icon pistons, 9:1, Eagle rods, Edlebrock alum heads, Cam? Roller Rockers) anyway i like the look of the original exhaust manifolds. Money is not an issue. Will headers make that much difference on a mild build like this? This will be going in a 1957 Super 88 coupled w/a 4L80E Trans. Thanks in advance for the help.!

 

My guess is long tube headers would be worth 15hp easily assuming you have a decent free flowing exhaust.

 

It depends on what your trying to accomplish and the look your after.

 

Apples to apples more like 30. BTR did a stroker big block Olds with manifolds vs headers, almost 50 hp difference. The more cubes or mods the more difference they will make.
But wondering why you're going to run Edelbrocks with manifolds anyway. Kind of defeats the purpose don't you think?
At the very least I'd run shorties.

 

My 2 cents free flowing exhaust adds significant hp you want to get good air in quick to help with the combustion but on that same note you want to expel that exhaust just as quick so headers would be your best choice for a mild build

 

Is clearance an issue?, What is it going into?. Headers win hands down for performance and releasing as much power as possible. But if you have to fabricate or modify them just to get it all in the engine bay then you may need to compromise.

Roger.